Javascript Object

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While lists are a useful method of storing data, they are inconvenient to use when you want to store multiple properties on a specific object in the list. For example, if you want to store data on all cookies sold in a cookie store, you need to create multiple lists to store the data.

is where the elements come in. Objects allow you to store data in name: value pairs, which means you can add labels to the data you have stored in your application

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In this guide we will discuss what and how objects are. you can use them in your code. We will talk about creating objects, modifying objects and deleting objects in the JavaScript programming language.

What is an object?

An object is a type of data in JavaScript. It is made up of names and values ‚Äã‚Äãzero or more, which are paired together. Each name acts as a label for a value. This means that if you want to access a particular value in an object, all you have to do is refer to the label. Names are sometimes referred to as "keys".

A value can contain any type of data, be it a string, number, or other object. Values ‚Äã‚Äãcan also contain properties and methods, which are functions applicable to a particular object.

Keys and values ‚Äã‚Äãare mapped together to create a key:. Pair of values ‚Äã‚Äãin a JS object.

JavaScript objects are the concept upon which JSON (which stands for JavaScript Object notation) was built. Although JSON is slightly different from JavaScript, both of these data structures use the name: even value method to store data

How to create an object

There are two ways to create an object: you can use the constructor approach of the object or declare a literal object

The object constructor uses the "new" word - key to create a new object:

This creates an empty object to which we can add values. We can also declare an object using a literal object, which is simply a set of braces:

In these two examples, we’ve created an empty object. You will find these methods used interchangeably in JavaScript applications. The literal object method is perhaps more common because of its simplicity; you just need to create a set of braces

To create an object with data, we can use the object literal syntax:.

This object contains four names and values. For example, the "price" tag is associated with the floating point number 1.50. The label "available‚" is associated with the Boolean value "true‚".

How to read an object

So far we have discussed how to create an object, but an object is not very useful if you cannot access it its content. There are two ways to read the contents of an object. You can use the period notation (.) Or the notation in parentheses ([]).

Let’s say we want to retrieve the name of our chocolate chip cookie. We could do it using this code:

This code returns: white raspberry chocolate chips. In our example, we’ve spoken the name of our object - "raspberry_white_choc" - followed by a period, the name of the property whose value we want to retrieve. This is why it is called point notation . There is a period between the object and the property name

You can also use the notation in parentheses to read an object:

Our code returns: .. true the notation in parentheses allows you to specify the name of an object, then the name of the value you want to retrieve the name of the value you want to recover must be enclosed in quotes, then square brackets

How to edit an object

There are three possible ways that you can edit an object:

Let’s discuss a by one, referring to our cookie example above.

Add elements to an object

A d if inference from lists, there is no push () or append () you can use to add a value to an object. All you have to do is assign a new value to a property using the assignment operator.

Let’s say we want to add the value "gluten free" to our object. We could make using the one of the following instructions:

Nos code returns:

In these two examples we created a new element in our object called "gluten_free.‚" The value we assigned to this element is "false.‚"

Modifying elements of existing objects

Modifying the Content of an object works the same way as assigning new values ‚Äã‚Äãto an object. Both methods use the assignment operator to change the subject.

Either to say it, we changed our recipe to the Raspberry White Chocolate Chip Cookie and is gluten free now. We could change the "gluten-free" element in our object using this code:

Our code returns: true. If you prefer, you can also use the parenthesis notation to make this change

Remove elements from an object

The keyword "remove" allows you to remove a property the age of an object. The following code will remove the "gluten_free" property of our object:

Our code returns:

As you can see, the name" gluten_free "is no longer present in our object because we used the word - delete key to delete it.

Conclusion

storing the structure of the JavaScript object data l iées In this article we talked about how an object could re- information about a cookie for a cookie shop. We could also have used an item for store user accounts, bakery recipes, or civilian tasks.

Javascript Object __del__: Questions

__del__

How can I make a time delay in Python?

5 answers

I would like to know how to put a time delay in a Python script.

2973

Answer #1

import time
time.sleep(5)   # Delays for 5 seconds. You can also use a float value.

Here is another example where something is run approximately once a minute:

import time
while True:
    print("This prints once a minute.")
    time.sleep(60) # Delay for 1 minute (60 seconds).

2973

Answer #2

You can use the sleep() function in the time module. It can take a float argument for sub-second resolution.

from time import sleep
sleep(0.1) # Time in seconds

__del__

How to delete a file or folder in Python?

5 answers

How do I delete a file or folder in Python?

2639

Answer #1


Path objects from the Python 3.4+ pathlib module also expose these instance methods:

Javascript Object __delete__: Questions

2639

Answer #2


Path objects from the Python 3.4+ pathlib module also expose these instance methods:

2639

Answer #3

Python syntax to delete a file

import os
os.remove("/tmp/<file_name>.txt")

Or

import os
os.unlink("/tmp/<file_name>.txt")

Or

pathlib Library for Python version >= 3.4

file_to_rem = pathlib.Path("/tmp/<file_name>.txt")
file_to_rem.unlink()

Path.unlink(missing_ok=False)

Unlink method used to remove the file or the symbolik link.

If missing_ok is false (the default), FileNotFoundError is raised if the path does not exist.
If missing_ok is true, FileNotFoundError exceptions will be ignored (same behavior as the POSIX rm -f command).
Changed in version 3.8: The missing_ok parameter was added.

Best practice

  1. First, check whether the file or folder exists or not then only delete that file. This can be achieved in two ways :
    a. os.path.isfile("/path/to/file")
    b. Use exception handling.

EXAMPLE for os.path.isfile

#!/usr/bin/python
import os
myfile="/tmp/foo.txt"

## If file exists, delete it ##
if os.path.isfile(myfile):
    os.remove(myfile)
else:    ## Show an error ##
    print("Error: %s file not found" % myfile)

Exception Handling

#!/usr/bin/python
import os

## Get input ##
myfile= raw_input("Enter file name to delete: ")

## Try to delete the file ##
try:
    os.remove(myfile)
except OSError as e:  ## if failed, report it back to the user ##
    print ("Error: %s - %s." % (e.filename, e.strerror))

RESPECTIVE OUTPUT

Enter file name to delete : demo.txt
Error: demo.txt - No such file or directory.

Enter file name to delete : rrr.txt
Error: rrr.txt - Operation not permitted.

Enter file name to delete : foo.txt

Python syntax to delete a folder

shutil.rmtree()

Example for shutil.rmtree()

#!/usr/bin/python
import os
import sys
import shutil

# Get directory name
mydir= raw_input("Enter directory name: ")

## Try to remove tree; if failed show an error using try...except on screen
try:
    shutil.rmtree(mydir)
except OSError as e:
    print ("Error: %s - %s." % (e.filename, e.strerror))

__delete__

Is there a simple way to delete a list element by value?

5 answers

I want to remove a value from a list if it exists in the list (which it may not).

a = [1, 2, 3, 4]
b = a.index(6)

del a[b]
print(a)

The above case (in which it does not exist) shows the following error:

Traceback (most recent call last):
  File "D:zjm_codea.py", line 6, in <module>
    b = a.index(6)
ValueError: list.index(x): x not in list

So I have to do this:

a = [1, 2, 3, 4]

try:
    b = a.index(6)
    del a[b]
except:
    pass

print(a)

But is there not a simpler way to do this?

1055

Answer #1

To remove an element"s first occurrence in a list, simply use list.remove:

>>> a = ["a", "b", "c", "d"]
>>> a.remove("b")
>>> print(a)
["a", "c", "d"]

Mind that it does not remove all occurrences of your element. Use a list comprehension for that.

>>> a = [10, 20, 30, 40, 20, 30, 40, 20, 70, 20]
>>> a = [x for x in a if x != 20]
>>> print(a)
[10, 30, 40, 30, 40, 70]

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